As is known, motor vehicles are equipped with safety belt restraint systems that are operable to physically restrain both forward and lateral motion of a seat occupant during a collision. Such safety belt restraint systems typically include a lap belt and a shoulder belt which, in most modern vehicles, are combined into a single seat belt. In such safety belt systems, one end of the seat belt is typically anchored to the frame of the motor vehicle at a location near the floor pan while the opposite end of the seat belt is coupled to a seat belt retractor that is mounted to the vehicle frame at the base of a support pillar (i.e., B-pillar). It is also common to mount a guide ring near the top of the support pillar so that the belt emanating from the seat belt retractor is initially routed upward along the pillar and looped over the guide ring to ensure that the shoulder belt is properly routed over the shoulder and upper torso of the seat occupant. In addition, a tongue plate is typically attached to the seat belt between the guide ring and the first anchor point for latched engagement with an anchored seat belt buckle.
Modernly, most safety belt restraint systems are of the emergency locking type and employ a locking mechanism which is operable to automatically shift the seat belt retractor from a "released" mode into a "locked" mode when the motor vehicle is subjected to deceleration forces exceeding a predetermined threshold level, thereby inhibiting subsequent withdrawal (i.e., "payout") of the belt webbing from the retractor. During normal vehicle operating conditions, however, the locking mechanism is adapted to maintain the seat belt retractor in its "released" mode such that the belt webbing may be controllably withdrawn therefrom. In some applications, the locking mechanism is an electrically-controlled solenoid actuator that is operable to shift the seat belt retractor into the "locked" mode in response to detection by a suitable sensor of an excessive vehicular deceleration condition. Alternatively, an inertia-sensitive locking mechanism may be integrated into the seat belt retractor. Such emergency locking retractors (ELR) are widely used in many conventional safety belt restraint systems since they provide improved comfort, convenience and freedom of movement for the seat occupants. An example of an emergency locking retractor equipped with a pendulum-type inertia-sensitive locking mechanism is disclosed in commonly owned U.S. Pat. No. 5,121,887 to Schmidt et al.
While conventional seat belt retractors equipped with such emergency locking mechanisms generally perform satisfactorily for their intended purpose, they must, however, be designed and built to accommodate extremely high and abrupt belt loading conditions. For instance, the tension loading exerted on the shoulder belt by the seat occupant during a collision or heavy braking condition is ultimately transferred to the guide ring and the seat belt retractor. As such, the structural load-bearing requirements for the guide ring and the seat belt retractor, as well as for the vehicular frame structure of the support pillar at the guide ring anchor site and at the retractor mounting site, must be capable of withstanding instances of such severe belt loading.
In an effort to minimize the belt loading that is ultimately transferred to the seat belt retractor, it has been proposed to incorporate a belt clamping mechanism into the safety belt restraint system for applying a clamping force on the belt webbing at a location upstream of the emergency locking mechanism. One example of such an arrangement is disclosed in U.S. Pat. No. 5,211,694 to Sakakida et al wherein the belt clamping mechanism is mounted to the retractor assembly. Alternatively, it has also been proposed to locate the belt clamping mechanism in close proximity to the guide ring. Examples of belt clamping mechanisms associated with a shoulder belt guide ring are disclosed in U.S. Pat. Nos. 4,494,774 to Fohl; 4,550,951 to Apri; 4,682,791 to Ernst; 4,747,617 to Magyar et al; 4,756,554 to Tibbe; 4,786,079 to Wyder; 4,993,746 to Hagelthorn; and 5,160,167 to Fourrey et al. While such auxiliary belt clamping mechanisms are designed to fulfill their intended purpose, most are relatively complex in structure and/or expensive to manufacture.